Process of tanning leather and article made thereby



A ril 23, 1935. F. WAYLAND 1,998,567

PROCESS OITANNING LEATHER AND ARTICLE MADE THEREBY Filed Jan. 12, 1952 Y I 1 i6' r10 IT\ X-\- a -1 I- *'i!J is 13 I 1 r F iu jivezzfoz' 5'- mx we e Patented Apr. 23, 1935 UNITED STATES PROCESS OF TANNING LEATHER AND ARTICLE MADE THEREBY Frank Wayland, Salem, Mass.

Application January 12, 1932, Serial No. 586,175

12 Claims.

My present invention relates to the art of tanning hides or skins, and consists in an improved method or process of tanning, and an improved article of manufacture made by my process.

In my prior U. S. Patent No. 1,430,479 I have disclosed and claimed a method of taming which consists in putting the hides'to be tanned under a stretching tension and holding the same under such tension during certain steps in the tanning process. That invention was of great importance because by its practice an increase in area is produced in the resulting leather to the extent of 20%, or even 30%, and more, over that obtained by ordinary tanning methods previously used. As the superficial area and measurement of leather are controlling factors in its value, this very substantial increase in the area was of great importance.

Two limitations, however, were found in carrying out the invention of my said prior patent, one being that it was diiiicult to produce leather of high quality when the hide was stretched and held under tension during tanning, and the other being that the process seemed to be limited to the grain side of split leather only.

taining the advantage of the increased area of my said former invention, and of the highest grade and quality, and am now enabled to take advantage ofthe large increase in area obtained by tanning in this manner, and also of the other incidental improvements and economies disclosed below.

I have been able to effect this satisfactory and improved result by employing a greater concentration and also a vastly greater amount of chrome or other metallic tanning material for a given quantity of hide substance to be tanned than was ever before used or considered possible by those interested in tanning under tension dur-' 'ing the years since the date of my original in vention disclosed in my said prior patent, or by tanners in general. Thus, for example, in tanning patent leather, for one pickled cow-hide grain split out of lime and weighing perhaps 25 pounds, I now use about 100 gallons of tan liquor 56' containing as much as l pound of chromic oxide,

CrzOa, per gallon, (representing 4 pounds per gallon of Tanolin, a well known commercial pre-- pared tan containing about 25% by weight of Cr-20a). Thus for 100 pounds of pickled stock I use more than 1600 pounds of Tanolin, whereas in the ordinary tanning methods about pounds of Tanolin (or the equivalent) would be used per 100 pounds of pickled stock, and in my prior work with tension tanning never more than A pound of Tanolin per gallon was used or about 100 pounds of Tanolin per 100 pounds of pickled stock.

Thus, by abruptly increasing the ratio of available tan to hide substance to a point 16 times as versed in the art and as can be seen by a study of my preferred method disclosed below, this large quantity of tan is not wasted or used up by the hides actually in contact with it, but it is used over and over again on other lots of hides, the concentration of tan being continually maintained by fresh additions. In fact, I-have found that the actual costs of tan are less by this process than by the ordinary tanning methods.

A further important feature is that my invention enables hides to be tanned and satisfactory leather to be'produced therefrom with increased area without necessarily splitting the grain surface from the rest of the hide.

Thus, in carrying out my preferred method, the hides, sides, splits, grains, or skins are prop erly prepared for chrome tanning, preferably as. drained pickled'stock. They are thereupon individually stretched out either on a board, in a framework; or otherwise, and are strained or stretched to desired extent and secured by tracks, air pressure, toggles, lacings, or any other means, or they may be stretched and a constant tension applied, as by means of a spring, to hold them in stretched condition and to efiect a still further stretching if desired.

These stretched hides on the boards, frames, or the likefmay then be immersed in a metallic tanning solution of high concentration, as above explained, or the solution may be otherwise applied as noted below. 1

Ordinarily, an operator can stretch out a pickled grain for patent leather, for example, using the usual tack pincers, to a point where 130 sq. ft. are made out of the grain obtained from pounds of green salted cow-hide. When desired, the entire grain may be tacked out with the backbone along the edge of the board and each half stretched and secured in stretched condition, or the sides may be tacked out, one on each side of the board. For this purpose, boards 12' long and 4 /2 wide would ordinarily be used, and a pit to hold 50 ata time would be 5' deep and 12 wide, and approximately 12 long, each board being preferably in a vertical plane when immersed in this pit.

As above noted, the stretched-out hides may have been shaved slightly if desired, -or split, or skived, using the grain only for tanning according to this method, particularly for patent or,

side-upper leather for shoe manufacture, or when smaller and lighter skins (calf, sheep, goat, etc.,) are used, the splitting or shaving, or other similar operations, may be omitted, although more area will be obtained and the stretch taken out of the skins, and they will be more uniform--that is, the thin flanks will be stretched less and the thick backs will .be stretched moreif even on these lighter skins some of the thicker parts of the skin are shaved before tanning, or

otherwim reduced in thickness. Moreover, shaving the flesh side of skins having ribby necks, or neck wrinkles, permits these wrinkles to bepulled out better and produces a smoother piece of leather.

The vat should contain a solution of prepared chrome tan containing one-half to one and a half pounds per gallon of chromium oxide. Where Tanolin, for example, is used, from two to six pounds per gallon would be employed equivalent to from 8 oz. to 20 oz. of chrome oxide. The temper ature of the vat and solution should be approximately 100 F. and the solution should completely cover the hides. After the immersion period, of from 30 to minutes, depending on the concentration of tan used and the chrome content desired in the leather, and the temperature of the liquor, the hides are lifted out of the vat, allowed to drain back, and the next lot to be tanned is lowered in the pit- Ordinarily, the hides, sides, splits, grains, or skins would then be removed from the boards or other supporting medium and be piled down smoothly on a platform or horse and left overnight in order to allow complete penetration of the tan into the individual fibres and to permit the'tan to set. In most instances, after this overnight settingthe leather can then be shaved without the usual pressing operation. At this point, the hides tanned under my method of stretching or tensioning are much firmer and less broken up than those put through the ordinary taming process in which they are tumbled about in a drum and, therefore, contain and hold less water and can be shaved without pressing. If desired, the hides can be left on the boards overnight, preferably being held at near 100 F., and near 100% relative humidity, and if desired, the rinsing and subsequent operations may be carried out while the hides are still on the boards.

Following the shaving, the leather as thus far manufactured, can be washed, neutralized, colored and fat-liquored in the usual conventional drums or paddles. However, work, handling, and expense can be reduced and the quality of the leather can be further. improved by avoiding all unnecessary drumming by simply hanging the hides on tenter-hooks, for example, and dipping successively into rinse water, preferably into a series of rinse waters in a counter current manner so as to build up and save and recover the accumulated chrome tan rinsed out of the hides, and then into further water containing a very small amount of bicarbonate of soda, or other alkali. The coloring and fat-liquoring opera.- tions as well can be accomplished, if desired, by similar dipping operations, or by spraying.

Thereafter, the hides may proceed through the usual subsequent finishing operations.

In practicing my invention I have found that it is not always necessary to employ a tank and to completely immerse the hides, grains, splits, sides, or skins in a bath of tan liquor, and that the same effect will be obtained if the hide prepared for tanning and held stretched out by any means is contacted with tan or has tan applied to the surfaces, and particularly to the flesh side, since penetration is much more rapid from that side, by any means, and further provided that the tan solution used is warm, concentrated, and of very much larger volume than that required to carry the amount of tan that is actually picked up by the hide. For example, dry powdered tan may be sprinkled on the moist drained pickled hide, or a thick paste of tan may be swabbed or brushed onto the flesh side and allowed to stand over night, and in the morning the excess may be rinsed off and saved for further use.

A series of fine spray jets of warm water (over 100 degrees F.) will do this effectively, since it is desirable to keep the volume of recovered tan solution .as small and as concentrated as possible. I have also found spray methods to be effective since chrome tan penetrates rapidly, and have used a fine spray from a nozzle with success although a more uniform result is obtained when the tan is applied with fine jets from a heated to over 100 F. (110 to F. depending on the fineness of the spray or jets) since spraying cools the liquid which impinges on the hide, and the finer the spray, the greater the cooling.

An automatic conveyor carrying hides while stretched out on suitable boards or frames, or the like, would reduce production costs in a large installation since the hides could move through a zone where either both sides of a toggled hide or side, or each of the two sides independently fastened on either side of a board or frame, would be sprayed or showered simultaneously, with an excess of warm recirculated concentrated tan liquor. In any of these spray methods it is important that a large excess of ten be contacted with the hide if leather of high quality is to be produced, so that the chrome content of the leather will be not only uniform but also sufficiently high. If just the right amount is applied there will be no driving force-difference in concentrationto carry sufficient tan into the center layers of the hide, and stiff, hard, parchment-like, under-tanned leather will result.

In ordinary tanning the drumming and pounding action of the wheels or drums forces tan in by causing an interchange of liquor between the inner cellular spaces of the hide and the outside liquor, much as happens when a sponge is squeezed under water. 'I'hllS whenthe liquor in the center of the hide becomes dilute due to the hide substance subtracting tan from it, it is replaced by more concentrated liquor by the iii pounding action in the drums. In tension tanning, by my preferred method in a large pit, the very large excess of tan in the pit, together with the high concentration cause a rapid interchange-due in part, no doubt, to osmosis and diffusion, and this is perhaps one reason for the markedly different final result when a concentrated solution is employed instead of a dilute solution.

In this disclosure, chrome tanning has been discussed but it will be easily understood by those well versed in the art that other metallic tans, such as aluminum or mixture of chrome and aluminum tans, such as are regularly used by tanners can also be used in this manner, and I do not wish to limit myself to chrome only. The various vegetable tans can also be employed when tanning under tension but this requires many special considerations and is the subject of a co-pending application.

The term concentrated tan solutions is used herein to denote concentrates greater than 1 pound of Tanolin per gallon A (Enos/gallon). If concentrates lower than this are employed the leather tends to be harsh and stiff and is really slack tanned and is unsuited for most purposes, although for embossed leather, which is preferably firm and a little stiff, a satisfactory product can be made with as low a concentration as A; pound of Tanolin per gallon.

Further important features and advantages of utilizing a concentrated tan is more fully de scribed and claimed broadly in the copending application of this applicant and Clarence K. Reiman, Ser. No. 608,850 filed May 2, 1932. It will be appreciated that in my present preferred method not only the method of tanning, but the amount and concentration of tan available and in contact with the hides and skins, or the like, during tanning varies but little from the beginning to the end of the tanning operation, that is, the amount of tan subtracted from the large volume of concentrated tan liquor available (when tanning a single lot of hides) is only a small part, about one-half per cent of the total in use, whereas in the ordinary methods, the concentration and amount of tan available towards the end of the tanning period. drops to a small fraction of that originally put into the wheel or paddle. This fact causes several real disadvantages in the prior art methods, to wit: The rate of tanning slows up, and eventually tanning stops altogether, while there is still a small excess of dilute residualtan solution in the wheel. This residual tan is wasted, high crome contents in the leather are difiicult and expensive to obtain since the higher the chrome content desired, the greater the amount of tan in the discarded tan liquor, and much drumming, which is detrimental to the stock and expensive as to power requirements,

must be done in order to force this rapidly diluted tan into the stock.

In this present application, I use the term hide generically and means to include hides, sides, grains, splits, skins with or without the hair, and the like. Where the terms raw hide, untanned hide, stock prepared for tanning are used I mean in general hides, or the like, ready for the application of the chrome tan, generally drained pickled stock, although I have used successfully without pickling both bated stock and stock out of lime that has been delimed with ammonium salts,- or lactic acid, or the equivalent, the largeexcess of concentrated tan liquor used in my process making the acidity of the stock of much less importance than in prior art methods of tanning.

The continued reuse of the large volume of concentrated tan liquor involves substantially a certain and positive control in order to maintain uniform conditions, which will be easily applied by those skilled in the art, although the following suggestions will perhaps make these points clearer. Accumulated dirt can be removed by filtering either continuously or at intervals by well understood methods; accumulated neutral salts (sodium sulphate is the chief salt impurity) can be removed by chilling the liquor, preferably continuously treating a small amount in a circulating system, thus causing the salt to crystallize and then filtering. Sulfuric acid may accumulate under certain conditions and may be neutralized with an alkali, such as sodium bicarbonate, and the resulting sodium sulphate removed, as above. Waste chrome liquor from many sources may be accumulated and concentrated by boiling and then treated as above, or the chrome may be precipitated with sodium bicarbonate, care being taken to avoid using excess, and the chrome precipitate, after separating from the mother liquor, may be redissolved if boiled up at once with an excess of the concentrated liquor taken from the tanning vat.

Clean dilute liquor can be used to dissolve fresh tan which must be added to the vat at regular intervals in order to maintain uniform concentration.

Leather of high chrome content is very desirable in many cases being soft, pliable and of good weight, and American tanners in'particular have found it both difficult and expensive to produce such leather by processes heretofore available due to the large losses of chrome tan, as discussed above. The chrome content of leather produced by my process may be anything desired, up to 6 or 7% or more, and may be regulated by the concentration of chrometan in the vat, the temperature of the liquor, the acidity conditions of the liquor in the vat, and of the stock prepared for tanning, and the length of time that the hides are immersed or otherwise contacted with the excess of warm concentrated tan liquor. Thus, after the tanner has chosen that set of conditions which gives him the chrome content and other characteristics desired in his leather, he has only to maintain these same conditions constant and he will continue to produce leather having these same characteristics with regularity.

The manner of handling and tensioning the hides will be apparent from the accompanying drawing in which,-

I Fig. l 'is a side elevational view showing a-hide stretched and secured to both sides of a frame or board;

Fig. 2 is a view illustrating a side stretched and tensioned to a frame, and

Fig. 3 illustrates the area of a normal side and that to which it can be stretched and tanned, thus maintaining it in its position of increased area by my present process.

As shown in Fig. l, a frame or board designated generally as I, is. prepared of suitable area to take the large-sized hides. frame would ordinarily be 12 long and 5' wide. In handling a full hide, the backbone of the hide 2 is fitted along the upper edge, secured by tacks 3, and then each side is stretched by the operator with the usual pincers and tacked in place.

As shown in Fig. 3, the normal area of a hide is indicated at 4, and the stretched. or tensioned As above noted, such a.

area at 5, this being typical and for illustrative purposes only. The hide 2, therefore, when thus stretched is secured by tacks 6 and the opposite side or half is similarly secured, as indicated in dotted lines 1 on the opposite side of the board. The hide thus under tension and held in its stretched position then goes through the tanning processes above explained.

As shown in Fig. 2, a framework I is provided and a toggle line l2, with toggles l4 to engage the side l5, each toggle line being attached rigidly at IE to part of the frame. This permits great flexibility in stretching the hide in various ways, as, for example, as indicated by the cross toggle lines l8 and 20, securing tension in the desired line of stretch. The toggle lins may be, if desired, elastic, as of springs or rubber, to exert a constant pulling tension on the hide or skin in the position where it is stretched to desired increased area.

The hide then goes through the tanning operations above described.

It will thus be appreciated that I have developed a method of tanning which permits a hideto be increased in area during the tanning and yet overcomes the objections heretofore found with such a method because of the presumed impossibilityrof making good leather-out ofsuch a hide during stretched condition. My improvement is of great importance and has rendered the invention of my said prior Patent No. 1,430,479 successful commercially, and I wish to claim the novel features of, the present invention herein broadly.

An improved product produced by my present invention comprises a pliable finished leather with all the advantages of being tanned under tension, eliminating wrinkles, increasing the area, and with practically all capacity for stretching eliminated.

I claim:

1. That improvement in the art of tanning leather which consists in applying a stretching tension to the hide to be treated, holding the hide in its tensioned condition, and applying thereto a I tanning solution containing a relatively concen trated chrome tan liquor containing more than 100 pounds of chrome oxide per 100 pounds of drained pickled hide.

2. The improvement in the art of tamiing hides, skins, or the like, whether split, shaved, skived, or otherwise, which consists in applying tension to substantially all parts of the same to stretch the fibre thereof to substantially the limit permitted without injury, increasing the superficial area and thereupon subjecting the hide, skin, or the like so stretched and held to the application of chrome tan material containing not less than twenty-five pounds of chromium oxide per hundred pounds of hides, skins, or the like to be treated.

3. The improved process of preparing leather from raw hides which consists in permanently increasing the area of a hide by subjecting it to a radial stretching tension, holding the same so tensioned, applying the tanning material to the hide while so held in stretched condition, including a highly concentrated tanning solution which on analysis would show a chrome content, as chrome oxide, of more than three per cent, and thereafter completing the washing, coloring, and finishing in the usual manner.

4. An article of manufacture, relatively soft and pliable leather having its fibres stretched to an extent rendering it substantially stretch-free,

and containing more than four percent of CrzO-a.

5. The method of tanning which is characterized by the steps of first tensioning the untanned skin or hide and then contacting it with concentrated metallic tan liquor in such quantity that the residual tan in the used liquor represents more than the amount picked up by the tanned product.

,6. The method of tanning which is characterized by the steps of first tensioning the untanned skin or hide and then contacting it with preheated concentrated chrome tan liquor in such a large quantity that the residual tan in the liquor exceeds substantially the amount removed by the tanned product.

7. The method of tanning in which a supply of chrome tan liquor is utilized over and over again in contact with successive lots of skins or hides held under tension and is of such composition that less than 50% concentration is lost in tanning each lot.

8. The method of tanning in which chrome tan liquor is used to contact successive lots of skins or hides held under tension, the liquor being in quantity and composition such that its concen tration may be maintained uniform by adding less than 50% make-up tan. after the treatment of each lot.

9. The method of tanning characterized by the step of treating skins or hides held under tension with a tan liquor of such composition and volume that the concentration of the liquor in contact with the stock remains substantially constant without the addition of fresh tan during the tanning process.

10. The method of tanning characterized by the step of treating skins or hides held under tension with a preheated chrome tan liquor of such com position that the concentration of the liquor in contact with the stock remains substantially constant during the tanning process.

11. The method of tanning characterized by the step of treating skins or hides held under tension with a chrome tan liquor of such composition and amount that, in the liquor in' contact with the stock, the concentration of chrome tan is not reduced more than 50% during the tanning process.

12. The method of chrome tanning which is characterized by the steps of first tensioning the stock and then contacting it with a concen-' trated chrome tan liquor in a quantity so great that the basicity of the liquor is not substantially reduced by the acid diflused into it from the stock and which can be used over and over again without requiring adjustment of its basicity.

FRANK WAYLAND. 

